The reason is because it implies you are generally more competent than they are, and should be paid attention to more. They are jealous and afraid they are going to lose attention from their friends to you because you have more to offer in terms of wisdom.
It really is that simple. Jealousy is an ignorant, worthless emotion.
A well rounded person who is funny, intelligent, attractive (as much as they can be), caring and successful probably will get attention and there isn’t much you can do about it. However, such a person doesn’t really want to hurt you or take things away from you anyways. They can only choose one mate, and only have a certain amount of time to interact with friends. And for people like this, generally the more the merrier (more funny comments, attractive people around etc) They want you to be successful to so they can have more successful friends and resources.
If a successful person is lacking in these other traits, you can call them out on it (to their face) and totally be in the right. Honest confrontation (not an outburst of anger or petty rumor-mongering) is the best course of action in that case.
How is it we can constantly be exposed to profound characters in media (movies, tv, books and even news) in this information age and yet petty insecure rumor-mongering behavior that is ridiculed in such media is still considered valid in real life?